Method to reduce magnetic film stress for better yield

ABSTRACT

A method of forming a thin-film deposition, such as an MTJ (magnetic tunneling junction) layer, on a wafer-scale CMOS substrate so that the thin-film deposition is segmented by walls or trenches and not affected by thin-film stresses due to wafer warpage or other subsequent annealing processes. An interface layer is formed on the CMOS substrate and is patterned by either forming undercut trenches extending into its upper surface or by fabricating T-shaped walls that extend along its upper surface. The thin-film is deposited continuously over the patterned surface, whereupon either the trenches or walls segment the deposition and serve as stress-relief mechanisms to eliminate adverse effects of processing as stresses such as those caused by wafer warpage.

BACKGROUND

1. Technical Field

This disclosure relates generally to magnetic devices that utilize thinfilm fabrications on wafers, and more specifically, to methods forreducing defects in such fabrications that result from stresses in thefilms and warpage of the wafers during processing.

2. Description of the Related Art

Spin torque memory based, for example, on MTJ devices, is believed to bescalable down to characteristic technology dimensions on the order of 65nm and even below. As the technology scales down, the budget for overlaydesign margins (i.e., room for error) will shrink correspondingly.Magnetic film depositions and annealing processes, for example thoseused in fabricating MTJ devices) normally introduce significant waferwarpage due to stresses in the films. Currently, most MRAM technologydevelopment is done on 200 mm wafers or smaller. When the technology isscaled down to 65 nm, the wafer warpage problem will be magnifiedbecause only the 300 mm wafer platform will be available. A furtherdrawback of high stresses in the film depositions is the associatedproduction of defects, such as film delaminations, which are alreadyfrequently encountered. The severity of such defects increases with theincreases in annealing temperatures. There has been a recognition of thestress problem, as evidenced by U.S. Pat. No. 6,696,744 (Feygenson etal) and U.S. Patent Application 2010/0226042 (Nishimori et al). However,neither of these teachings provides a methodology for dealing with theproblem in the manner of the present disclosure.

The following brief and schematic description of a current process toform and process thin-film layered structures will indicate thedifficulties encountered. It is these difficulties that will beaddressed using the methods of the present disclosure.

Exemplary Current Process

Schematic FIG. 6 a, illustrates a first step in an exemplary currentprocess. Its corresponding first process step is described briefly inthe first box (1) of the process flow chart of FIG. 2. FIG. 6 a (and box(1) of FIG. 2) shows, schematically, in cross-section, a “last metallayer” (50) of a CMOS substrate (full substrate not shown) that willhave an MTJ multi-layered deposition (not yet shown) formed over itsupper surface and thereby be connected to the CMOS devices andassociated circuitry within the substrate. It is to be noted that inthis and in all the following descriptions we use the phrase “last metallayer” to refer to an uppermost layer of a CMOS substrate. This lastlayer contains the metal, electrically conductive connections that willbe made to multi-layer thin-film depositions that will be deposited onthis last layer of the substrate. When we refer more generally to a CMOSsubstrate, we mean a substrate that contains within its body CMOScircuitry that would be used to activate the thin-film, multi-layeredMTJ devices (formed on its “last metal layer”) such as those in an MRAMarray. However, it should also be pointed out that the general approachdescribed herein to forming a thin-film multi-layered deposition thatwill not be subject to defects resulting from process-induced stressescould apply equally well to other wafer-sized substrates that incurwarpage when subjected to thermal processes and to other thin filmdepositions of sufficient size to experience stresses and stress-relateddefects when formed on such substrates.

The CMOS last metal layer (50) is the uppermost layer of the CMOSsubstrate (not shown) and it will be assumed to be the starting layerfor subsequent process steps in all the methods described herein. It isalso assumed, for simplicity, that the CMOS last metal layer includes asegmented, electrically conductive (e.g. metal) connection layer (70)within its upper surface, surrounded by structurally supportive andinsulating dielectric material (75), and that the connection layer (70)will ultimately contact appropriate portions of theabout-to-be-fabricated MTJ deposition through an interconnecting layercalled (in block (2) of FIG. 2) a “connection via & interface layer”. Itis further assumed that these same conducting connection layers (70)lead to CMOS circuit elements in the CMOS substrate that is beneath thelast metal layer. These connections will not be shown herein, however,and the last metal layer will serve to represent all CMOS circuitry inthe substrate.

Referring next to the illustration of FIG. 6 b and to the description inthe second process step of block (2) in FIG. 2, there is illustrated anddescribed a second current process step in the fabrication of an MTJlayer, which is to build a connection via and interface layer which willserve to connect the subsequent MTJ fabrication to the last metal layer((50) of FIG. 6 a) and, thereupon, to the CMOS circuitry. A conductingvia (80) is shown above each connecting layer segment (70), each viapassing through a first dielectric layer (90), which is an etch-stoplayer, and a second dielectric layer (95), which is an interface layer,and terminating at a junction connection (105) that will ultimatelycontact appropriate portions of an MTJ thin-film deposition. Thestructure now completed on the last metal layer, including elements(90), (80), (95) and (105) is the “connection via & interface layer”described in bock (2) of FIG. 2. A detailed description of the mode offabrication of this layer will not be described herein, but new forms ofthis layer will be described in detail below.

Referring now to FIG. 6 c and to the remaining process sequence in FIG.2, process boxes (3) and (4), describe, sequentially, the formation ofan alignment layer (the zero-layer) and a continuous MTJ film depositionon the fabrication of FIG. 6 b. In FIG. 6 c, the alignment layer and theMTJ film are indicated as a single layer (120), which would typically beformed as two separate but contiguous layers.

Referring finally to FIG. 2, process steps of blocks (5)-(7), there isdescribed a series of exemplary processes performed on the alignmentlayer and MTJ film (120), including, for example, an anneal, aphoto-patterning (e.g. deposition of a photo-resist layer or equivalentphoto-lithographic emulsion) and a subsequent etch. It is thesesubsequent processes that, in the current practice, will be associatedwith wafer warpage and defects in the MTJ film (120). In the processesto be described below, methods for eliminating these defects will bedescribed.

SUMMARY

A first object of the present disclosure is to provide a method forreducing or eliminating defects in thin film depositions on wafersresulting from wafer warpage and process-induced stresses in thedeposited MTJ films.

A second object of the present disclosure is to provide increasedmargins for overlay errors produced by wafer warpage and thin filmstresses in the MTJ films, where such errors are accentuated byshrinking technology dimensions and use of larger wafers.

A third object of the present disclosure is to implement the first twoobjects in as efficient a manner as possible and with a minimum ofadditional process steps.

The present disclosure achieves these objects by means of the creationof stress-relief trenches within an interconnect and interface layer, orthe formation of stress-relief walls on an interconnect and interfacelayer, on which interconnect and interface layer an MTJ film issubsequently formed, processed and patterned.

In the present disclosure, an interconnect and interface layer providesa mechanism for electrically connecting MTJ thin-film depositions to anunderlying CMOS substrate (or equivalent wafer-level substrate). Thetrenches or walls then create a breakage of the MTJ film into discrete,separated and disconnected segments whereby stress-relief is obtained.This process can be implemented using two basic methods and associatedvariants that will be fully described below:

First Method. Patterning a connection and interface layer formed on aCMOS substrate with an array of undercut trenches formed before (orafter) the MTJ magnetic film deposition. These trenches act asstress-relief mechanisms by segmenting the film.

Second Method. Patterning a connection and interface layer formed on aCMOS substrate with an array of T-shaped walls that act as dividers andthen depositing an MTJ film over the interface layer and dividing walls.These dividers act as stress-relief mechanisms by segmenting the filmand they can be subsequently removed.

The approach of the first method, above, is implemented by the creationof trenches with undercut profiles. Such trenches break the subsequentlydeposited metal TMJ films into smaller, isolated segments. FIG. 1 is aschematic illustration of a deposition-covered wafer (5) showing anexemplary horizontal (in the wafer plane) pattern of intersectingvertical (through the plane) trenches (10) that has served tosub-divide, into discrete segments (20), a multi-layered deposition thatwould otherwise have continuously covered the entire wafer surface.

The generation of patterns of trenches having undercut profiles, or thefabrication of similar patterns of T-shaped dividers, both involve thedeposition of multi-layer dielectric films, such as films of SiN or SiO₂or low-k dielectric materials, with different etch rates for dry or wetetch methods. The etch rate for the deposited underlayer or underlayersare significantly faster than that for the top layer.

After deposition of dielectric layers, the wafer is photo-patterned,forming hard masks out of photo-resist and then etched. During theetching process, an undercut profile is achieved as a result of thedifferential between the etch rates of the dielectric underlayer andoverlayer, which will be shown below. The height (or depth) and lengthof the divider (trench) must be sufficient to break the continuity ofsubsequent MTJ film depositions.

Fabrication processes typically begin by deposition of a so-called“zero-layer” on which alignment marks and overlay boxes are created,before or after an MTJ film deposition. These zero-layer fabricationsallow the implementation of accurate photo-process alignments andoverlays (OL) on subsequent-layer depositions. It is herein proposed tocombine the stress-relief trench-creation layer and the zero-layer intoa single layer that performs both functions so no additional mask layeris required to implement the stress-relief process.

In a second method, T-shaped dividers are formed prior to an MTJ filmdeposition. These dividers can be removed after the MTJ film isdeposited by the use of etching or CMP methods.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration showing a circular wafer with anexemplary pattern of trenches in the wafer plane.

FIG. 2 is process flow diagram for an exemplary current process used topattern MTJ films.

FIG. 3 is a process flow chart for a first trench-forming process (FirstMethod, Variations A, B and C) designed to meet the objects of thepresent disclosure.

FIG. 4 is a process flow chart for a wall-forming process (SecondMethod) designed to meet the objects of the present disclosure.

FIG. 5 is a process flow chart for yet an additional alternativetrench-forming process (Third Method) designed to meet the objects ofthe present disclosure.

FIGS. 6 a, 6 b and 6 c schematically illustrate (in wafercross-sectional views) three steps in a physical implementation of theprocess steps of the current process flow diagram of FIG. 2.

FIGS. 7 a-7 n schematically illustrate (in wafer cross-sectional views)fourteen steps in a physical implementation of the process steps of theprocess flow diagram of FIG. 3 (First Method, Variation A) showing theformation of an undercut (inverted-T shaped) trench.

FIGS. 8 a-8 g schematically illustrate (in wafer cross-sectional views)seven steps in a physical implementation of the process steps of theprocess flow diagram of FIG. 3 (First Method, Variation B) showing theformation of an undercut (trapezoid-shaped) trench.

FIGS. 9 a-9 e schematically illustrate (in wafer cross-sectional views)five steps in a physical implementation of the process steps of theprocess flow diagram of FIG. 3 (First Method, Variation C) showing theformation of an undercut (trapezoid-shaped) trench.

FIGS. 10 a-10 i schematically illustrate (in wafer cross-sectionalviews) nine steps in a physical implementation of the process steps ofthe process flow diagram of FIG. 4 (Second Method) showing the formationof a T-shaped wall and subsequent processing of an MTJ deposition.

FIGS. 11 a-11 e schematically illustrate (in wafer cross-sectionalviews) five steps in a physical implementation of the process steps ofthe process flow diagram of FIG. 5 (Third Method) showing the formationof a trench.

DETAILED DESCRIPTION

The present disclosure describes methods by which multi-layered,thin-film devices (e.g. multi-layered thin magnetic film MTJ devices)can be fabricated on a wafer substrate (e.g. a CMOS substrate) so thatthe multi-layer thin-film deposition is not affected by defects due tostresses in the deposited thin-films caused by wafer warpage andsubsequent annealing processes. A first and third method, with severalvariants, breaks the thin-film deposition, which would otherwise coverthe entire wafer, into smaller isolated segments. This is done byforming a pattern of undercut trenches into a connection via andinterface layer on which the multi-layer, thin-film deposition is thenformed. These trenches, which are of various cross-sectional shapes,then serve as stress-relief mechanisms.

A second method also creates a stress-relief mechanism, but in thismethod it is done by forming T-shaped dividers that serve as walls alongthe upper surface of the connection via and interface layer, before themulti-layer thin-film deposition occurs. In either of the methods, forefficiency of the process, the role of the stress-relief layer (whetherused for forming trenches or walls) is efficiently combined with the“zero-layer” that normally serves to provide an alignment or overlaymechanism for subsequent photo-lithographic patterning schemes.

First Method, Variation A

Referring now to the new process steps of FIG. 3 and the correspondingillustrations in FIGS. 7 a-7 n, there will be described and illustratedthe process steps of a first method (Variation A) leading to theformation of a pattern of undercut trenches in a via connection andinterface layer that will implement a stress-relief mechanism and breakan overall MTJ thin-film deposition into discrete, separated pieces thatare free of stresses. Note that, for simplicity, the formation of anarray of trenches is illustrated using an exemplary single trench, whichwould be a part of the array. Therefore, the resulting thin-filmdeposition is shown as being segmented into two portions, while, inpractice, it would be segmented into portions bounded by the array oftrenches (or walls in the subsequent method).

Referring first to block (1) of FIG. 3 and to FIG. 7 a, there is shown a“last” CMOS metal layer (50) that is the same as layer (50) of FIG. 6 a.This “last,” or uppermost layer of the CMOS substrate represents thesubstrate level on which the process steps begin.

Referring next to the description in block (2) of FIG. 3 and theillustration of FIG. 7 b, there is shown a sequence of three dielectriclayers that will be used to construct a connection via and interfacelayer (shown finally completed in FIG. 7 i) between the last metal layer(50) and a subsequent MTJ deposition (to be shown below in FIG. 7 n).

Layer (200) is an etch-stop layer, layer (210) is an “embedded” highetch rate layer (called “embedded” because it will have an intermediateposition within the final structure) and layer (205) is a dielectriclayer that will form the insulating and supportive structure of theinterface. The thickness of the high etch rate (210) layer can rangebetween approximately 20 nm and 200 nm. The high etch-rate dielectricmaterial of (210) can be SiN, SiO₂, or any spin-on dielectric materialsor low k materials. It will be used to form the undercut portion of thetrench. The designation “high etch rate,” is to be understood here andin all of the following in a relative sense. The process described willwork properly as long as there is a selectivity of 4 or higher in theetch rates between the embedded layer (210) and an overlayer (e.g.interface dielectric layer (205)). Generally, in all the following, thecandidates for the high etch-rate materials can be oxygen plasma ornitrogen plasma etchable materials such as amorphous carbon, porousdielectric materials and other spin-on filler dielectric materials. Thetop layer, of less high-rate etchable materials, can be formed of SiN,SiO₂ or other materials that are normally not etchable by oxygen ornitrogen plasma.

Referring now to process step (3) of FIG. 3 and to FIG. 7 c, there isshown the formation and patterning (openings (225)) of a photo-resistlayer (220) formed on layer (205) of the previous fabrication of FIG. 7b. This photo-resist layer will form a hard mask to allow the formationof vias by means of an etching process through the patterned openings.

Referring now to FIG. 7 d, there is shown the result of applying anetching process through the patterned openings (225) of FIG. 7 c to formcorresponding openings (226) for conducting vias. The etch process canbe a dry etch, a wet etch or a combination of the two that allowspenetration to the connection layers (70).

Referring now to FIG. 7 e, there is shown the formation of vias (227) byfilling the etched openings with a conducting material, such as a metal.The vias electrically contact the segmented connection layers (70) inthe last CMOS layer. The dielectric interface layer (205) is thensmoothed and thinned, along with the vias, using a CMP process.

While still within the descriptive portion of FIG. 3 block (2) andreferring to FIG. 7 f, there is shown the fabrication of FIG. 7 e withthe addition of a deposition of an additional metal interface layer(300).

Referring next to FIG. 7 g there is shown a second patternedphoto-lithographic film (310) (e.g. photoresist) formed over the metalinterface layer (300). This film will act as a hard-etch mask.

Referring next to FIG. 7 h, there is shown the results of an etchingprocess on the metal interface layer ((300), of FIG. 7 g), leavingbehind conducting pads (320) electrically contacting the vias (227).

Referring now to FIG. 7 i, there is shown the fabrication of FIG. 7 hwith the addition of a blanket dielectric deposition (330), which isplanarized and rendered co-planar with the surfaces of the conductingpads (320). The additional blanket layer is materially identical todielectric overlayer ((205) in FIG. 7 b) and the two layers togethercombine to form the interface layer (330) of the fabrication. Thisfabrication is now the completed connection via and interface layerdescribed as to be built in process box (2) of FIG. 3. We will now usethis layer fabrication (or its equivalent in FIG. 8 b, FIG. 9 b, FIG. 10b and FIG. 11 b) as a starting point for forming the stress-reliefmechanism of trench or wall. This fabrication would also serve as thezero-layer for subsequent masking and overlay processes as required forthe MTJ layers.

Referring now to FIG. 7 j, there is shown the deposition of an optionalprotective layer (352) over the fabrication of FIG. 7 i.

Referring now to process box (3) of FIG. 3 and FIG. 7 k, there is shownthe first process step in the formation of a stress-relief trench in theconnection via and interface layer fabrication of FIG. 7 i. In thisstep, a third photo-lithographic (photo-resist) layer (345) is depositedto form a hard-mask and then etched to form an opening (350) throughwhich a trench will be formed. The opening will have an approximatewidth of 20 nm.

Referring to FIG. 7 l, there is shown the results of a third etchprocess through hard-mask opening (350) of FIG. 7 k, now forming acorresponding opening (305) of uniform width in the dielectric layer(330) reaching to the depth of the high etch rate layer (210). The hardmask layer (345) is then removed.

Referring to FIG. 7 m, there is shown the results of an additionalfourth etch (or the continuation of the third etch), which significantlywidens an undercut opening (307) in the high etch rate layer (210)compared to the width of the opening (305) which remains substantiallythe same in its width because of its slower etch rate. As was alreadynoted above, the thickness of the high etch rate (210) layer can rangebetween approximately 20 nm and 200 nm. Preferably the width of theundercut portion (307) etched in this layer should be greater thanapproximately 20 nm (the width of the opening in the dielectricoverlayer) to effectively break the continuous deposited MTJ layer intoseparated segments as will be shown below in FIG. 7 n. It can be seenthat the shape of the trench, in vertical cross-section, is an invertedT, formed from the openings (305) and (307). It is understood thatopening (305) and (307) extends linearly along the upper surface of theCMOS layer as in FIG. 1, perpendicular to the plane of the precedingfigures and that the illustration shown in these figures are verticalcross-sections of the opening.

Referring now to process step (4) of FIG. 3 and illustration FIG. 7 n,there is shown the formation of what would be a continuous MTJ film,(400), over the fabrication of FIG. 7 m. The trench, (305) and (307),however, has effectively separated the MTJ film into two isolatedportions (500) and (600), which can now be subjected to the furtherprocessing steps (e.g. patterning and annealing) described in FIG. 3(5)-(7), while being resistant to the effects of stresses induced bythose steps because of the stress-relief furnished by the free ends(510) and (610) of the isolated portions where they intersect the trenchwalls.

First Method, Variation B

Referring again to the process steps of FIG. 3, while now observingcorresponding illustrations in FIGS. 8 a-8 g, there will be describedand illustrated the process steps of a First Method, Variation B leadingto the formation of a pattern of undercut trenches that will alsoimplement a stress-relief mechanism and break the overall MTJmulti-layer deposition into discrete, separated pieces that are free ofstresses. These undercut trenches, however, have a trapezoidal verticalcross-sectional shape that is unlike the inverted T of Variation A andare formed using a somewhat different sequence of process steps thatwill now be described.

Referring first to process step (1) of FIG. 3 and to corresponding FIG.8 a, there is shown a last CMOS metal layer (50) that is the same aslayer (50) of FIG. 6 a and FIG. 7 a. It represents the starting point ofthe process.

Referring next to the process description in block (2) of FIG. 3 and theillustration of FIG. 8 b, there is shown a connection via and interfacelayer that has been fabricated almost precisely according the sequenceof illustrated steps already shown previously in FIGS. 7 b-7 i, howeverthose steps are not shown now because of their repetitious nature.

The fabrication in FIG. 8 b is a connection via and interface layer thatis virtually identical to that shown previously in FIG. 7 i, except thatthe two layers (205) and (210) of FIG. 7 b; with different etch ratecharacteristics (high and low etch rates) have now been replaced by asingle layer (205) with a single etch rate characteristic. Etch-stoplayer (200) remains. All process steps shown in FIGS. 7 b-7 h have beenrepeated to form FIG. 8 b, except separate layer (210) was neverdeposited and is not needed in the subsequent steps. This fabrication ofFIG. 8 b is now the analog of the connection via and interface layer inFIG. 7 i, which is described as to be built in process box (2) of FIG. 3in order to connect a CMOS substrate to an MTJ film.

Referring now to FIG. 8 c, there is shown the deposition of a protectivelayer (350) over the fabrication of FIG. 8 b. The protective dielectriclayer will be formed of a dielectric material with a lower etch ratethan that of the interface dielectric layer (205) which has a high etchrate (approximately 4 times the etch rate of the protection layer). Aphoto-resistive layer (355) is formed over layer (350) and patterned toopen a region (357) of approximately 20 nm width through which astress-relief trench will be formed.

Referring now to FIG. 8 d, there is shown the first process step in theformation of a stress-relief trench in the fabrication of FIG. 8 c. Inthis step a dry etch process creates an opening through protective layer(350) using layer (355) of the previous FIG. 8 c as a hard mask. The dryetch is shown as having continued to remove a portion of layer (205).

Referring now to FIG. 8 e, there is shown the continuation of the dryetch process, or the switch to a wet etch process, to etch further intolayer (205). The presence of the protective layer (350) now causes thedry (or wet) etch to create a trench with an undercut profile (375)because the dielectric layer (205) etches more rapidly than theprotective layer (350) above it. The trench cross-section is shown astrapezoidal, but it is understood that this shape is exemplary of anundercut region that expands laterally with depth vertically.

Referring now to FIG. 8 f, there is shown the results of applying asecond etch process to remove the protective layer ((355) of FIG. 8 e).

Finally, FIG. 8 g shows the fabrication of FIG. 8 f, with the formationof an MTJ film, (400), over the fabrication of FIG. 8 f. The trench,(375) has effectively separated the MTJ film into two isolated portions(500) and (600), which can now be subjected to the further processingsteps described in FIG. 3, blocks (5)-(7), while being resistant to theeffects of stresses induced by those steps because of the stress-relieffurnished by the free ends (510) and (610) of the isolated portionswhere they intersect the trench walls.

First Method, Variation C

Referring again to the process steps of FIG. 3, while now observingcorresponding illustrations in FIGS. 9 a-9 e, there will be describedand illustrated the process steps of a First Method, Variation C leadingto the formation of a pattern of undercut trenches that will alsoimplement a stress-relief mechanism and break the overall MTJmulti-layer deposition into discrete, separated pieces that are free ofstresses. These undercut trenches have a trapezoidal verticalcross-section that is like that of Variation B above, and unlike theinverted T form of Variation A. They are formed using a somewhatdifferent sequence of process steps than those of Variation B, that willnow be described.

Referring first to process step (1) of FIG. 3 and to corresponding FIG.9 a, there is shown a last CMOS metal layer that is the same as layer(50) of FIG. 6 a, FIG. 7 a and FIG. 8 a. It represents the startingpoint of the process.

Referring next to the process description in block (2) of FIG. 3 and theillustration of FIG. 9 b, there is shown a connection via and interfacelayer, like that of FIG. 8 b, that has been fabricated according to thesame sequence of illustrated steps leading to the formation of FIG. 8 bas previously discussed.

Referring now to FIG. 9 c, there is shown a fabrication analogous tothat shown in FIG. 8 c except that the protective layer (350) over thefabrication of FIG. 8 c is absent. Instead, FIG. 9 c shows aphotoresistive layer (355) that is formed directly over the uppersurface of the fabrication of FIG. 9 b and is patterned to open a region(357) of approximately 20 nm width through which a stress-relief trenchwill be formed.

Referring now to FIG. 9 d, there is shown the first process step in theformation of a stress-relief trench in the fabrication of FIG. 9 c. Inthis step a dry or wet etch process creates a trench (in a directionperpendicular to the plane of this figure) with an expandingcross-section through the patterned photo-mask region (357) usingphotoresist layer (355) of the previous figure as a hard mask. Theetched region descends vertically and is stopped by etch-stop layer(200). The trench cross-section is shown as trapezoidal, but it isunderstood that this shape is exemplary of an undercut region thatexpands laterally with depth vertically. The layer of photoresist isthen removed using an etchant.

Finally, FIG. 9 e shows the fabrication of FIG. 9 d, with the formationof an MTJ film, (400), over the fabrication of FIG. 9 d. The trench,(375) has effectively separated the MTJ film into two isolated portions(500) and (600) (a small portion also shown at the bottom of thetrench), which can now be subjected to the further processing stepsdescribed in FIG. 3 (5)-(7), while being resistant to the effects ofstresses induced by those steps because of the stress-relief furnishedby the free ends (510) and (610) of the isolated portions where theyintersect the trench walls.

Second Method

Referring now to the process flow steps of FIG. 4, while observingcorresponding illustrations in FIGS. 10 a-10 i, there will be describedand illustrated the process steps of a Second Method, leading to theformation of a pattern of walls, rather than trenches, that will alsoimplement a stress-relief mechanism and break the overall MTJmulti-layer deposition into discrete, separated pieces that are free ofstresses.

Referring first to process step (1) of FIG. 4 and to corresponding FIG.10 a, there is shown a last CMOS metal layer that is the same as layer(50) of FIG. 6 a, FIG. 7 a, FIG. 8 a, and FIG. 9 a. It represents thestarting point of the process.

Referring next to the process description in process block (2) of FIG. 4and the illustration of FIG. 10 b, there is shown a connection via andinterface layer identical to that in FIG. 8 b that has been fabricatedaccording the sequence of illustrated steps already shown previously inFIGS. 7 b-7 i, however those steps leading to the fabrication are notshown now because of their substantially repetitious nature.

The fabrication in FIG. 10 b is virtually identical to that shownpreviously in FIG. 7 i, except that the two layers (205) and (210) ofFIG. 7 b, with different etch rate characteristics are not required inthis process sequence, so they have now been replaced by a single layer(205) with a single etch rate characteristic. All process steps shown inFIGS. 7 b-7 i have been replicated to form the fabrication of FIG. 10 b,except separate layer (210) was never deposited. This fabrication ofFIG. 10 b is now the analog of the connection via and interface layer inFIGS. 7 i and 8 b, which is described as to be built in process box (2)of FIG. 4 in order to connect a CMOS substrate to an MTJ film.

Referring now to process step (3) of FIG. 4 and to a correspondingschematic illustration in FIG. 10 c, there is shown the first step inbuilding a wall on the upper surface of the fabrication of FIG. 10 b. Tothis end, two material layers, (170) and (180), with different etchrates are deposited on the top of the fabrication. The low etch-ratelayer (180) is deposited over the high etch-rate layer (170). As in theprevious discussion, “high” and “low” as referring to etch rates arerelative terms referring to an etch-rate selectivity of a factor of 4between the two layers.

Referring next to FIG. 10 d, there is shown a patterned photo-resist(190) formed on the uppermost layer (180) of the two dielectric layers.This film will serve as an etch mask.

Referring next to FIG. 10 e, there is shown the results of an etchingprocess performed on the masked fabrication of FIG. 10 d. The upperdielectric layer ((180) in FIG. 10 d) has been etched away laterallybeyond the width of the remaining patterned film ((190) in FIG. 10 d)leaving a horizontal base (185). The dielectric layer ((170) in FIG. 10d) has been etched away even further, because of its higher etch rate,leaving a narrow pedestal (175) supporting the wider base (185). Thestructure of the base and pedestal has an approximately T-shapedcross-section. It is further understood that the T-shaped structureextends across the entire CMOS substrate (see FIG. 1) linearly in adirection perpendicular to the cross-sectional plane, so that the base(185) and pedestal (175) have the aspect of a wall that will create theseparation of the deposited MTJ layer.

Etchants for the higher etch-rate layer ((170) in FIG. 10 d) can beoxygen or N₂ plasmas and the corresponding material for that layer canbe any material that etches rapidly under these etchants, such asamorphous carbon, porous dielectric material and other spin-on fillermaterials. These materials must also have a high etch-rate selectivityas compared to the dielectric materials (205) used in forming theconnection and interface layer, and the upper layer dielectric material(180). The upper layer (180) can be a layer of SiN, SiO₂ or any othermaterial that does not etch using an oxygen plasma.

Referring next to FIG. 10 f, there is shown the results of an MTJ filmdeposition (400). Although the film has been deposited continuously overthe entire fabrication, the vertical extension of the base/pedestalcombination (185)/(175) causes the film to separate into two disjointportions (500) and (600) (a small portion remaining on top of (185)).These two disjoint portions will not be susceptible to stress relateddefects resulting from subsequent processing steps, such as those to benow shown, and will therefore meet the objects of this disclosure.

Referring next to FIG. 10 g, there is shown the first of a sequence ofsteps for further processing of the deposited MTJ film portions (500)and (600). First a BARC (bottom anti-reflective coating) or dielectriclayer (710) is spun on over the fabrication of FIG. 10 f. This layer isthen planarized. It is noted that the connection via and interface layeris effectively serving as a zero-layer in that it provides a substratefor masking operations used to define structures of the MTJ layer.

Referring next to FIG. 10 h, there is shown a patterned photo-resistlayer (220) (a mask) formed over the BARC or dielectric layer (710).

Referring next to FIG. 10 i, there is shown the two MTJ portions ((500)and (600) of FIG. 10 g) patterned into separated segments (430), eachsegment now electrically contacting a connection pad (320), a via (80)and, ultimately, CMOS segment (70). It is to be noted that although thismethod has utilized an initial layering of two dielectric layers (170)and (180) of unequal etch rates to create the T-shaped base/pedestalstructure (175)/(185) that breaks the MTJ deposition, it is alsopossible to create a T-shaped structure using a single layer depositedfilm.

Third Method

Finally, there is now described a third method for separating adeposited MTJ film using a simpler trench formation method. Referringagain to the process steps in the flow chart of FIG. 5, while observingcorresponding illustrations in FIGS. 11 a-11 e, there will be describedand illustrated the process steps of this method.

Referring first to process step (1) of FIG. 5 and to corresponding FIG.11 a, there is shown a last CMOS metal layer that is the same as layer(50) of FIG. 6 a, FIG. 7 a, FIG. 8 a, and FIG. 9 a. It represents thestarting point of the process.

Referring next to the process description in process block (2) of FIG. 5and the illustration of FIG. 11 b, there is shown a connection via andinterface layer that is identical to that in FIG. 8 b. There is shownthe conducting pads (320), the interlayer dielectric (205) and theetch-stop layer (200).

Referring now to process block (3) of FIG. 5 and to FIG. 11 c, there isshown the connection via and interface layer that is the completedfabrication of FIG. 11 b, onto whose upper surface an MTJ film (400) hasbeen continuously deposited.

Referring next to process block (4) of FIG. 5 and to FIG. 11 d, there isshown a photo-resist film (700) that has been formed directly on the MTJfilm (400) and patterned to form an opening (750). This will be used asa hard mask. The opening (750) has been formed in the photo-resist filmwith sufficient width (approximately 20 nm) to allow etching of acorresponding opening through the MTJ film (400) to form a stress-relieftrench.

Referring finally to FIG. 11 e, there is shown the result of a dry orwet etch that has formed the corresponding opening through the MTJ filmand continued to form a trench (215) in the interface dielectric layer(205) of the connection via and interface layer. The two segments (500)and (600) of the separated MTJ film can now be further processed whileremaining in a stress-free state.

As is finally understood by a person skilled in the art, the preferredembodiments of the present disclosure are illustrative of the presentdisclosure rather than limiting of the present disclosure. Revisions andmodifications may be made to methods, materials, structures anddimensions employed in forming and providing a stress-relief mechanismfor an MTJ deposition by a pattern of walls or trenches and theresulting stress-free MTJ deposition so patterned, while still providingsuch a process and fabrication in accord with the spirit and scope ofthe present disclosure as defined by the appended claims.

What is claimed is:
 1. A thin-film deposition comprising: a substrate: apattern of trenches formed in the substrate; a multi-layered thin-filmdeposition formed on said substrate, wherein said thin-film depositionis broken into segments by said pattern of trenches and wherein saidthin-film deposition is subsequently processed; whereby process-inducedstresses are relieved by said pattern of trenches; and said thin-filmdeposition is free of defects normally caused by said process-inducedstresses.
 2. The thin-film deposition of claim 1 wherein said substrateis a CMOS substrate on which is formed a connection via and interfacelayer and wherein said thin-film deposition is an MTJ deposition.
 3. Thethin-film deposition of claim 2 wherein said CMOS substrate includes alast metal layer and wherein said connection via and interface layer isformed on said last metal layer and wherein said pattern of trenches isformed in said connection via and interface layer.
 4. The thin-filmdeposition of claim 1 wherein said trenches extend vertically into saidsubstrate and increase in width laterally as they penetrate verticallyto acquire an undercut vertical cross-sectional shape.
 5. The thin-filmdeposition of claim 2 wherein said MTJ deposition has been separatedinto non-contiguous independent segments.
 6. The thin-film deposition ofclaim 3 wherein said MTJ deposition has been separated intonon-contiguous independent segments.
 7. The thin-film deposition ofclaim 4 wherein said undercut trench has a narrow portion of widthapproximately 20 nm formed in a first dielectric material having a lowetch rate and a wide portion of width between approximately 20 nm and200 nm formed in a contiguous second dielectric material having a highetch rate.
 8. The thin-film deposition of claim 7 wherein said seconddielectric material is the high etch rate material amorphous carbon,porous dielectric material or other spin-on filler materials that etchrapidly under N₂ or oxygen plasmas and wherein said first dielectricmaterial is SiN, SiO₂ or any other material that does not etch using anoxygen or N₂ plasma.